Well, leveling up can get tedious. I recommend turning your regular units into Squires and learning the Accumulate ability (from the Squire's skillset) as soon as possible. This skill not only raises your physical attack power slightly, it also counts as an action, and as such, practically gives you free Exp/JP. Ramza should learn Accumulate and Yell as soon as possible, and later on, Scream. Now leveling up and gaining extra JP shouldn't be too much of a problem. Also, Yell raises the target's speed, so you can use the Knight's Speed Break on a lone enemy, raise your turns and lower its turns, and then Accumulate until you have as much JP as you want! This is tedious, but really, the alternative would be much more so.
Eh...anyway, good luck!
Edit: I recommend learning 'Throw Item' for your Chemist ASAP, and then just start learning more and more items and then maybe make him a Mage character. Then, he'll be able to heal your teammates with Item as a secondary skill combined with Throw Item for extra range.
For the rest of your characters, well, they're all up to you. I usually made Ramza mostly melee classes, and kept two or three mages with the special characters for a team.